This invention relates to a constant velocity joint for use in a motor vehicle. Note particularly, this invention relates to an encapsulated spring for the constant velocity joint.
Constant velocity joints have been used in the transportation industry for years. These constant velocity Joints can be separated into two classes, fixed joints and plunge joints.
Fixed joints have a fixed center of rotation and have a large angular capability (45.degree.-50.degree.). These joints are usually found at the wheel side of front wheel drive vehicles. The large angular capability of the joint allows the wheel to turn during steering maneuvers.
Plunge joints have a movable center of rotation and are somewhat limited in their angular capability (20.degree.-25.degree.). These joints are usually found at the differential end of front wheel drive vehicles. The angular and plunging capabilities accommodate suspension movement, engine movement and center line changes induced by the geometry of the suspension system during suspension movements.
A typical front wheel drive vehicle has a plunge joint connected to a fixed joint by an interconnecting shaft. This combination of joints is referred to as a halfshaft. There is normally a pair of halfshafts on each vehicle. One for the right hand side and one for the left hand side. These halfshafts drive the wheels and thus rotate at wheel speed.
A similar configuration of halfshafts can be found on most rear wheel drive vehicles with independent rear wheel suspension. The only difference in a rear wheel drive vehicle is that the wheels do not accommodate steering. For these vehicles, it is possible to use two plunge joints for each halfshaft. When using two plunge joints, a mechanism is necessary to position the interconnecting shaft with respect to the two plunge joints. Generally, this is accomplished by providing centering springs between the interconnecting shaft and the plunge joints.
For rear wheel drive vehicles and four wheel drive vehicles, propshafts, which rotate at engine speed, are used to carry the power from the transmission or transfer case to the front or rear differentials. The engine speed is normally greater than the wheel speed due to differential and transmission gear ratios. Propshafts also utilize constant velocity joints to provide the required angular and plunge travel. When two plunge joints are used in a propshaft arrangement, the arrangement requires a mechanism to center the interconnecting shaft. The mechanism is similar to those used in independent rear wheel drives. As mentioned above, centering springs may be used to accomplish the centering.
One design of a centering spring includes a coil spring located in a pocket of the plunge joint outer race. One end of the coil spring rests against the bottom of the pocket and the other end is attached to a metal cup. The metal cup bears against the interconnecting shaft. An identical configuration is used in the joint at the opposite end of the halfshaft or propshaft. The interconnecting shaft is free to float between the two plunge joints, however, it will always be positioned by the reaction of the two centering springs to a position which equalizes the preload on both springs.
One disadvantage encountered with this type of spring centering design, and particularly with the propshaft application, is to maintain the position of the spring between the joint outer race and the interconnecting shaft. As the joint rotates, the spring extends and compresses as the interconnecting shaft floats between the two joints. When the spring is in its extended position, centrifugal force tends to disengage the spring and cup from the interconnecting shaft.
Additional disadvantages are encountered when balancing the halfshaft or propshaft prior to vehicle installation. Normally only propshafts are balanced due to their high speed operation. The unpredictability of the position of the centering spring, due to the centrifugal forces acting on it, produces an inconsistent amount of out of balance and an inconsistent location of out of balance. Thus it is difficult to accurately determine how large of a balancing weight should be applied as well as where it should be placed.
Accordingly it is desirous to have a centering spring which would be less susceptible to the centrifugal forces produced during rotation in order to better balance the assembly. Likewise, it is desirous to have a high degree of confidence that the integrity of the assembly will be maintained during its life.